Selective removal of benzene from spent sulfur absorbents

ABSTRACT

As an improvement to processes for desulfurization of natural gas and synthetic natural gas streams that employ conventional zeolitic materials (absorbents), including copper-containing zeolites, pre-treatment methods and post-treatment methods are provided that lower the level of leachable benzene following desulfurization with the absorbents to &lt;0.5 mg benzene/L leachate, while retaining within the absorbents a majority of sulfur adsorbed from a gas stream.

CROSS REFERENCE TO RELATED U.S. APPLICATION

This patent application claims the benefit of priority to U.S.provisional patent application Ser. No. 62/576,706 with a filing date ofOct. 25, 2017, the full contents of which are fully incorporated hereinby reference in their entirety.

FIELD OF INVENTION

Present embodiments address and solve a significant problem related todesulfurizing gas streams by adsorption onto absorbents (includingwithout limitation zeolitic material), by virtue of reducing benzenelevels that would otherwise be contained on the absorbents.

BACKGROUND

Natural gas, a source of hydrogen fuel, is a colorless and odorlesscombustible gas, and it provides an abundant fuel source that iscommonly used in stationary fuel cell applications. Practical uses offuel cells range from stationary industrial power supplies to portablepower for consumer electronics. In many parts of the world, natural gasand synthetic natural gas (collectively, “natural gas”) are madeavailable through an extensive pipeline distribution network thatdelivers the fuel to homes and businesses, including fuel cellmanufacturers. Any leak in this pipeline network may pose a significantrisk of gas accumulating to explosive levels without detection.

To reduce this risk, odorants are added to the natural gas which allowsindividuals to detect natural gas leaks without any equipment. The mostcommon odorants used are sulfur compounds that have odors similar torotten eggs or cabbage. These compounds vary by region, but typicalexamples include: mercaptans, sulfides, disulfides, thiophenic compoundsand other organic or inorganic sulfur compounds. Problematically, thesulfur in such sulfur-containing compounds is a poison to most reformingand low temperature shift catalysts commonly found upstream of fuelcells, as well as most fuel cells themselves. Thus, it is necessary toremove the sulfur odorants at a point in the process before the naturalgas is used as fuel for the fuel cell.

Two types of desulfurization are commonly used for fuel cellapplications: ambient temperature and hot (typically 200-400° C.)desulfurization. In ambient temperature desulfurization, absorbents suchas zeolites are often used to remove sulfur compounds primarily byphysisorption. Chemisorption can occur on zeolitic materials for somecompounds, such as hydrogen sulfide (H₂S), but to a lesser extentcompared to the physisorption. As these zeolitic materials removecompounds primarily based on size and shape of the molecules, they alsoremove hydrocarbons from the gas stream in addition to thesulfur-containing compounds. This is of little consequence for most ofthe hydrocarbon compounds, with the noted exception of benzene. This isa particular concern in many countries, including in the U.S., where thespent absorbent must be disposed as hazardous waste if the absorbentleaches >0.5 mg benzene/L of leachate as defined by the EnvironmentalProtection Agency's (EPA) Toxicity Characteristic Leaching Procedure(TCLP). For fuel cell applications, the benzene not captured by theabsorbent is normally reformed or oxidized depending on the application.Thus, only the benzene trapped on the absorbent is of concern.

Accordingly, present embodiments improve processes for desulfurizationof natural gas, including ambient temperature desulfurization, whichinclude those processes that use conventional zeolitic materials asabsorbents. The improvements lower the level of leachable benzene at endof life (EOL) of the absorbent to <0.5 mg benzene/L leachate, whileretaining the majority of sulfur adsorbed onto the zeolites. In thisregard, present embodiments utilize the differences in binding strengthand binding mechanisms for the relevant sulfur compounds and benzene.For example, one prior study reported findings on nonaromatic andsaturated aromatic organosulfur compounds adsorbed on ion-exchangedzeolites (including Cu—Y zeolite). Velu, Xiaoliang and Song in“Mechanistic Investigations on the Adsorption of Organic SulfurCompounds Over Solid Adsorbents in the Adsorptive Desulfurization ofTransportation Fuels”, Am. Chem. Soc., Div. Fuel Chem. 2003, 48(2), 693.The authors observed that the mechanism of adsorption tends to occur bymetal sulfur (M-S) interactions, whereas benzene is adsorbed by weakerπ-complexation. In particular, the study pointed out that non-saturatedaromatic sulfur compounds such as thiophene tended to bind to thezeolites either by direct M-S interaction or π-complexation. Arecognition that such differences exist between sulfur compounds andbenzene has advantageously and unexpectedly led to strategies forblocking, displacing or otherwise removing a substantial amount ofbenzene from used or spent absorbents.

SUMMARY OF EMBODIMENTS

Absorbents are required to remove sulfur odorants from pipeline naturalgas for use in fuel cell operations, as these sulfur compounds arepoisons to many catalysts and fuel cells. However, benzene also canaccumulate on these absorbents during operation, requiring end of lifedisposal as hazardous waste. Accordingly, embodiments provided hereinallow the in-situ selective removal of benzene from these absorbents,thus promoting compliance with EPA limits for disposal of used or spentsulfur absorbents as non-hazardous waste, in accordance with theToxicity Characteristic Leaching Procedure (TCLP).

The strategies used in selective removal of benzene from sulfurabsorbents will vary based on circumstances. In general, though, benzenecontent in used or spent absorbents has been lowered through variousmechanisms, including: extraction, in which a solvent (e.g., benzylalcohol, methanol) dissolves benzene and transports it away duringevaporation; displacement, in which a compound (e.g., sulfur compoundsdescribed herein, water) that bonds directly with copper found in theabsorbent displaces the benzene molecules; or reaction, in which acompound reacts with the copper, liberating the benzene as it pulls thecopper from the zeolite cages (e.g., benzaldehyde and butyraldehyde.)

According to multiple embodiments and alternatives described herein, thepurpose of the post-treatment (i.e., following desulfurization, justbefore or after removal of the absorbents from the reactor) of sulfurabsorbents will dictate the selection of strategy in terms of whichcompound/mechanism is preferred. For example, there are scenarios inwhich very low leachable benzene (TCLP benzene) levels are required,coupled with little to no concern of corrosion or poisoning of theabsorbent because it will not be reused. Such factors would tend toincrease the effectiveness of benzaldehyde, for example, as apotentially viable post-treatment option. By comparison, given theobjective of reducing the TCLP benzene to <0.5 mg/L leachate withoutcorroding or poisoning the zeolite absorbents, water in both the liquidand gaseous phases is a suitable post-treatment compound, and providesthe further advantage that it is an environmentally benign substance.

Accordingly, there are provided in some embodiments a pre-treatmentmethod, which expose the absorbents to agents that are not classified astoxic, which interact chemically with the absorbents via the sameπ-complexation mechanism as benzene. The chemical interactions therebyserve to block benzene from chemical interaction between electrons ofπ-orbitals of aromatic benzene and metal contained in the absorbents.

Additionally, according to some embodiments, a post-treatment methodpracticed upon the absorbents displaces at least a portion of thebenzene attracted to the absorbents due to chemical interaction betweenelectrons of π-orbitals of aromatic benzene and metal contained in theabsorbents. In some embodiments, the displacement of benzene isselective in that the agents that displace benzene from the absorbentsdo not in turn displace—or these agents only minimally affect thebinding of—other molecules and compounds that have bonded to orinteracted with the absorbents, such as sulfur compounds.

Pre-treatment refers to exposing and applying to the absorbents one ormore agents before use and under the conditions described, eitherin-situ or ex-situ relative to the reactor in which the absorbents areinstalled according to known techniques. In the reactor, the absorbentsare then contacted with a particular gas stream, such as pipelinenatural gas, in which the natural gas contains sulfur compounds andaromatic hydrocarbons such as benzene. Conversely, post-treatment refersto exposing and applying to the absorbents either in-situ or ex-situ,one or more agents under the conditions described herein after theabsorbents have been removed from service or prior to their reuse. Forpre-treatment and post-treatment, treating of the absorbents in-situ(while in the reactor) is preferred, but both forms of treatment alsocan occur outside the reactor where desulfurization occurs.

In some embodiments, one or more agents used for pre-treatment orpost-treatment is diluted, e.g., with methanol. Additionally, in someembodiments one or more pre-treatment steps and one or morepost-treatment steps as described herein are practiced sequentially uponthe same absorbents.

Also, there are provided herein certain embodiments in whichpre-treatment is used on one region of an absorbent bed, whilepost-treatment is used on a different region of the same absorbent bed.In this regard, according to some embodiments, as selected by a user,pre-treatment is used upon absorbents making up an absorbent bed andpositioned more proximal to the inlet of the bed, because regions of theabsorbent bed closer to the inlet see higher concentrations of sulfurcompounds in the gas stream.

Additionally, according to at least one embodiment, the methods ofpre-treatment or post-treatment, or both, as described herein areutilized on an absorbent bed that will be reused. Alternatively, any ofthese methods are practiced upon an absorbent bed that has reached itsend of life and will not be reused.

BRIEF DESCRIPTION OF FIGURES

The embodiments described and claimed herein will be further understoodin view of the following figures, which are intended as illustrativeonly.

FIG. 1 is a graph of sulfur and benzene loading profiles for acommercial desulfurization bed comprising absorbents.

FIG. 2 is a graph of TCLP benzene levels as a function of time on streamwith respect to a desulfurization bed as discussed for FIG. 1.

FIG. 3 is a photograph of an untreated absorbent after exposure to astream of natural gas containing hydrocarbons including aromatics, andsulfur compounds.

FIG. 4 is a photograph of an absorbent exposed to the same stream ofnatural gas as the absorbent of FIG. 3 and treated with benzaldehyde.

FIG. 5 is a photograph of an absorbent exposed to the same stream ofnatural gas as the absorbents in FIG. 3 and FIG. 4, again followingtreatment with benzaldehyde. The absorbent in FIG. 5 is from a differentpart of the absorbent bed, further upstream and closer to the inlet,compared to the absorbent in FIG. 4.

MULTIPLE EMBODIMENTS AND ALTERNATIVES

Present embodiments are directed to removal of benzene from absorbentsthat are used in the desulfurization of natural gas fuels. Sulfurizationenables the detection of leaks of natural gas pipelines, but the sulfurcontent must be removed prior to any use of the natural gas, such as ina fuel cell. However, the conventional absorbents used in removing thesulfur from natural gas also trap carbon compounds—including benzene.Benzene is a hazardous substance and must be lowered below specifiedlevels on the absorbent before the absorbent can be disposed of as anon-hazardous material.

Sulfur and Benzene Loading Profiles

As illustrated in FIG. 1, a typical benzene and sulfur profile for acommercial absorbent bed in which the absorbents are spent reflects aninverse relationship between the absorption of benzene and sulfurcompounds from a stream of natural gas. Moving from left to right alongthe horizontal axis of the figure, the bed inlet is 0% of the bed (i.e.,a point at which the gas stream has not yet traversed any portion of thebed) and the bed outlet is 100% of the bed (i.e., the point at which thegas stream has traversed the entire bed). Herein, a commercial absorbentbed is any of many types that are available from manufacturers in thiscountry and internationally. While not meant as limiting, an example ofsuch a commercial absorbent bed (as used in the examples containedherein) comprises a Cu—Y zeolite with about 7-13% copper oxide with muchof the balance as aluminosilicate zeolite, with trace amounts (<1,000ppm) of calcium, iron, and titanium. Such absorbents may have a densityof about 0.55 kg/L, a hardness rating of at least about 15 N, and anextruded particle size of about 1-10 mm, of which 1.6 mm particle sizehas been used in some embodiments.

In operation with such an absorbent bed, total carbon throughout the bedgenerally is fairly consistent, at about 7-10% wt. Looking at the twocurves (one for TCLP benzene and the other for % S), FIG. 1 illustratesthat the amount of total sulfur becomes more concentrated at the bedinlet and decreases moving through the bed, while the amount of TCLPbenzene is lowest at the bed inlet and increases moving through the bed.

FIG. 2 is a graph of TCLP benzene levels as a function of time onstream. The test conditions were performed at ambient temperature andatmospheric pressure, and a GHSV of 450 hr⁻¹. A feed gas comprisingPipeline natural gas (˜2.5 ppm tBM (tertiary butyl mercaptan), ˜1 ppmDMS (dimethyl sulfide), ˜1 ppm H₂S, 30-80 ppm benzene) was run over a 40mL bed volume. For the data in FIG. 2, absorbent samples were analyzedat different times on stream (i.e., resulting in different sulfurconcentrations). It is seen that TCLP benzene is highest early in therun as the sulfur concentration is low. With time on stream, the sulfurconcentration increases and the TCLP benzene decreases at a seeminglyexponential rate from 139 to 3.8 mg/L of leachate by 129 days on streamin this figure.

Binding Strength and Binding Mechanisms

Present embodiments recognize that the binding strength and bindingmechanisms relative to metal-containing absorbents are different formost sulfur compounds compared to benzene. For example, many sulfurcompounds exhibit direct metal-sulfur (M-S) bonding. Conversely, benzeneis held primarily by π-complexation between the metal and the electronsin the ring, with the M-S interaction being stronger than theπ-complexation. Accordingly, in some embodiments pre-treatment steps(before absorbents are exposed to a natural gas stream) are provided toblock benzene from interacting with the absorbents. In otherembodiments, post-treatment steps occur before or after the absorbentsare removed from the reactor having been exposed to a natural gasstream, and are provided to selectively displace benzene from theabsorbents while retaining the adsorbed sulfur compounds. That is, forthe latter it is possible to displace the benzene with molecules thatadsorb more strongly or by a different mechanism compared to benzene,such as direct metal bonding. For example, a post-treatment step is theselective reaction using one or more agents described herein thattargets the metal-benzene π-complex to displace benzene, while the M-Sbonds are minimally affected. This route achieves very low benzenelevels throughout the bed but requires the use of organic compounds.

Accordingly, in some embodiments a method is provided to lower benzenelevels in absorbents that are used for desulfurization of a gas flow ina reactor having an inlet and an outlet. The steps include applying atleast one agent to the absorbents, wherein the absorbents arealuminosilicate zeolites having a structure that contains at least onemetal, which can be copper. The agents displace a large amount of thebenzene that has interacted with the metal of the zeolite. In someembodiments, the at least one agent is benzyl alcohol, benzaldehyde,methanol, diethyl ether, or mixtures thereof. In some embodiments, theweight percentage of the at least one agent is about 30% to about 60%,and more particularly in some instances about 40% to about 50%. In thecase of benzyl alcohol, the weight percentage may range from about 10%to about 50%.

In some embodiments, the at least one agent is water, at a weightpercentage of about 1% to about 60%, preferably about 10% to about 50%.In some embodiments, the treatment uses water in a liquid phase appliedwith a sprayer. Alternatively, the water that is used is in a gaseousphase and applied as a hydrated gas stream.

In some embodiments, these methods as disclosed herein are performed atambient temperature. Alternatively, these methods are performed at atemperature no greater than about 100° C.

Pre-Treatment

Accordingly, in some embodiments, pre-treatment occurs beforedesulfurization of a gas stream using absorbents and refers to thepre-adsorption of compounds by the absorbents to block benzene. Data ontests conducted indicated that certain compounds can be pre-adsorbedonto an absorbent to block the benzene, while still allowing sulfuradsorption by the absorbent. The compounds studied included thoseranging from water to aromatic compounds with various functional groups.Pre-adsorption was accomplished by incipiently wetting the absorbentwith the desired pre-adsorbate (20-50% wt). The pre-treated samples werethen evaluated in natural gas for sulfur and benzene adsorption.

In some experiments, comparative data indicated that unsaturatedaromatics (e.g., ρ-xylene) were able to block benzene better thansaturated aromatics (e.g., cyclohexane), but neither was effectiveenough to allow the spent absorbent to be disposed as non-hazardouswaste at end of life (EOL). For aromatic compounds with differentfunctional groups, it was found that unsaturated aromatic aldehydes(e.g., benzaldehyde) and unsaturated alcohols (e.g., benzyl alcohol)were preferred over ρ-xylene and cyclohexane, respectively, to preventor limit benzene adsorption, <0.1 mg benzene/L leachate. However, bothof these aromatic compounds also negatively affected the adsorption ofsulfur as well. Therefore, benzaldehyde was diluted with methanol andapplied to the absorbent to achieve 1% wt benzaldehyde. This returnedonly some of the sulfur capacity and the benzene blocking was alsodiminished. Even so, this is not to say that benzaldehyde is not usefulas a treatment agent according to present embodiments, and further theinteraction observed between the absorbent and benzaldehyde led to otherinsights which are discussed below. Water and diethyl ether also wereevaluated as agents for pre-treatment, with diethyl ether showingstronger adsorption than water. However, at some levels (wt %), thesewere not indicated to have interactions with the absorbent strong enoughto prevent benzene adsorption.

The following descriptions by way of examples are intended to providerelevant and illustrative information pertaining to possible embodimentsof the present invention. No limitation of the breadth and scope of theoverall invention is to be construed by any examples provided hereinexcept as specifically recited in the claims.

The following tables show the TCLP benzene results at different GHSV andbed volume for various compounds.

TABLE 1 Treatment Loading, TCLP benzene, Agent wt % mg/L leachateUntreated N/A 13.00 Cyclohexane 36 7.86 ρ-Xylene 46 2.58 Benzaldehyde 470.07 Benzaldehyde 1.0 9.78 Test Conditions: Temp = Ambient Pressure = 5pounds per square inch gauge (psig) Bed volume = 10 mL GHSV = 10,000hr⁻¹ Feed Gas = Pipeline natural gas (~2.5 ppm tBM, ~1 ppm DMS, ~1 ppmH₂S, 30-80 ppm benzene).

The value for weight percentage (wt %) for the treatment agents in theexperiments described herein was calculated based on the ratio of theweight of the agent over the weight of the absorbents in the reactor.

TABLE 2 Loading, TCLP benzene, Sample wt % mg/L leachate Untreated N/A3.13 Water 48 3.06 Diethyl ether 50 1.93 Benzyl alcohol 41 0.01 TestConditions: Temp = Ambient Pressure = 5 psig Bed volume = 20 mL GHSV =8500 hr⁻¹ Feed Gas = Pipeline natural gas (~2.5 ppm tBM, ~1 ppm DMS, ~1ppm H₂S, 30-80 ppm benzene)

The bed volume and gas hourly space velocity (GHSV) are differentbetween the data sets shown in Table 1 and Table 2, which causes theTCLP benzene level for the untreated absorbents to be different in thetwo tables. This is consistent with lower benzene levels being foundwhen sulfur levels are higher. In other words, more sulfur is adsorbedby the absorbents at lower GHSV, which corresponds to lower TCLP benzenelevels in Table 2, compared to the results in Table 1 for higher GHSV.

Post-Treatment

Post-treatment refers to steps taken to affect the absorbents followingdesulfurization of the gas stream. As with the pre-treatment evaluation,data was collected on several of the compounds in the context ofpost-treatment. Criteria for viability include the extent to which acompound lowers overall TCLP benzene to <0.5 mg/L, while allowing theabsorbent to retain most of the sulfur absorbed. It has been observedthat sulfur concentration in the gas stream decreases moving from theinlet to the outlet of the bed, while the benzene level increases movingfrom the inlet to the outlet of the bed. It is believed the maximumbenzene level is reached very early in operation and continues todecrease with time on stream. Accordingly, different parts of the bedare expected to contain different levels of benzene.

The post-treatment evaluation was completed by incipiently wetting acommercially spent absorbent with the desired post-treatment compoundand placing the samples in a benchtop hood overnight to evaporate thecompound. Then TCLP benzene analysis was performed on the samples. Thebaseline spent sample used for this study was a commercially spentmaterial from the bed inlet containing a high sulfur level and lowbenzene level (B₁T₁). This provided a reasonable manner to evaluate theefficacy for benzene removal. This is because, as discussed furtherbelow, it has been found that it is more difficult to displace lowlevels of benzene from material containing high levels of sulfur. Thecompounds evaluated for post-treatment included benzaldehyde, benzylalcohol, diethyl ether, methanol and water. Water as a liquid and wateras a gas are used according to multiple embodiments, both aspre-treatment and post-treatment. Water as a liquid may be applied byspraying, and as a gas may be applied with a carrier gas. In someembodiments, nitrogen is one of several suitable carrier gases for waterand other agents described herein. Table 3 shows results for liquidphase post-treatment for TCLP benzene and % S retained by the absorbentfrom the commercially spent sample:

TABLE 3 Loading, TCLP benzene, % S Sample wt % mg/L leachate retainedUntreated N/A 1.06 100 Benzaldehyde 47 0.03 92.3 Methanol 45 0.55 94.9Water 48 0.43 99.8 Benzyl alcohol 41 0.41 89.5 Diethyl ether 50 0.5092.0

While not expected based on any reports in the literature of whichapplicant is aware, a reaction between the spent absorbent andbenzaldehyde during this post-treatment evaluation was observed, whichled to identification of several agents according to the presentembodiments, including benzaldehyde as pre-treatment for loweringbenzene levels on spent absorbents. When the sulfur level on the spentabsorbent was high (conversely, benzene level is low), no significantvisual change occurred upon the spent material post-treated withbenzaldehyde. By comparison, when the sulfur level on the spentabsorbent was low (conversely, benzene is high) a noticeable visualchange in the absorbent occurred, in that blue crystalline structuresbegan to form on and throughout the absorbent, along with shards ofwhite crystals. The blue crystals were most likely a result of coppermigration induced by the benzaldehyde, as it becomes oxidized to benzoicacid over the absorbent. Images taken with an optical microscope showedan untreated spent absorbent, a spent absorbent with low sulfur (highbenzene) that was post-treated with benzaldehyde, and a spent absorbentwith high sulfur (low benzene) post-treated with an equal amount ofbenzaldehyde at the same conditions. The low sulfur-high benzene,benzaldehyde-treated absorbent showed white crystals formed on the edgesand throughout the particle. The referenced images are reproduced in theFIGS. 3-5, with FIG. 3 representing untreated absorbent, FIG. 4representing low-sulfur high benzene absorbent treated with benzadehyde,and FIG. 5 representing high sulfur-low benzene absorbent treated withbenzaldehyde.

The images in FIGS. 3-5 and the data herein indicate that the Cu—S bondsare too strong to be broken by the benzaldehyde. By comparison, however,the π-complexation between copper and benzene is much weaker and able tobe broken by the interaction with benzaldehyde. Additionally, the “free”copper (copper not bound to sulfur) in the spent absorbent likelycatalyzes the oxidation of benzaldehyde to benzoic acid. For example,present embodiments are suitable to be practiced upon commerciallyavailable zeolite absorbents used for desulfurization of natural gas.Copper Y-zeolites are such an absorbent, and the material of theabsorbent bed for the testing described herein was made up of suchzeolites containing approximately 7-13% copper, and in some cases about10% copper.

It also was deduced that free copper migrating upon the absorbentcoalesces at different places along the structure, preventing furtherabsorption by the absorbent. This further explains the mixed results ofbenzaldehyde as a pre-treatment. The benzaldehyde reacted with copper onthe fresh absorbent, moving the copper out of the cages and preventingthe absorption of sulfur. This is different, however, from the loss ofsulfur capacity due to pre-treatment with benzyl alcohol. Benzyl alcoholhas a boiling point of 205° C., allowing it to remain as a liquid in theabsorbent pores and prevent absorption. Thus, at ambient temperaturesthe loss of sulfur capacity due to pre-treatment with benzyl alcoholresults primarily from physical obstruction.

Additionally, no evidence of the kind of reaction with benzaldehyde wasseen from pre- or post-treatment with benzyl alcohol. This was confirmedby post-treatment with the four-carbon chain analogues: butyraldehyde,butanol and butyric acid. Butyraldehyde and butanol showed similarresults to their six-member ring counterparts, where the aldehyde causedsignificant agglomeration of copper and the alcohol showed no impact.Surprisingly, there was no significant agglomeration of copper thatoccurred with the treatment of the carboxylic acid (butyric acid). Thisindicates that it is the actual oxidation of the aldehyde that frees thecopper and allows it to agglomerate, and not just dissolution andre-deposition of the copper by the carboxylic acid. At concentrationsbeyond those claimed here, benzaldehyde may have limitations as apre-treatment or post-treatment agent because it has the potential tocause several issues if it converts to benzoic acid: corrosion,plugging, and potential downstream poisoning. When benzaldehyde is to beused as a treatment agent at the end of absorbent life, however, thesefactors are less of a consideration. Further, the data and observationswith benzaldehyde also help to inform the mechanisms that influenceother post-treatment strategies as discussed herein.

Now concerning post-treatment with water, both liquid water and vaporphase water were included in testing. The data here showed that benzeneis more easily removed from the absorbents when the benzene level ishigh and the sulfur level is low (middle of bed, B₃T₁) with as little as1.5% H₂O in N₂ at ambient temperature (˜50% water saturation), as Table4 shows:

TABLE 4 TCLP benzene, Sample mg/L % S B1T1 Untreated 1.06 3.9 B1T1 1.5%H₂O in N₂ 0.97 4.0 B1T1 Liquid H₂O 0.43 3.7 B3T1 Untreated 14.3 <0.01B3T1 1.5% H2O in N₂ 0.02 — B3T1 3% H₂O in N₂ <0.01 —

By comparison, benzene is more difficult to remove when the sulfur levelis high and the benzene level is low (inlet of bed, B₁T₁) with only 50%water saturated gas. This is because the adsorbed sulfur inhibits theaccess of the water molecules to the sites where benzene tends to belocated. Higher levels of water saturation (˜100%) will be required tolower the benzene level when the sulfur level is high.

It should be noted, however, that the environmental standards discussedherein consider the bed as a whole rather than in particular segments ofthe bed. Therefore, heavily sulfur saturated portions of a bed mightremain close to limits for acceptable TCLP benzene levels, yet theoverall bed will test well within TCLP limits. Stated differently, evenwithout removing the majority of the benzene at the inlet of the bed,water vapor will lower the overall benzene level for the entire bedbelow the EPA limit of 0.5 mg/L leachate. Thus, the data obtained fromthese studies shows that post-treatment with water in either liquid orvapor phase is able to accomplish sufficient benzene reduction tosatisfy limits for disposal of sulfur absorbents as non-hazardous waste.Water saturated gas can be used to lower benzene levels below TCLPrequirement if liquid water cannot be used or is impractical.

It will be understood that the embodiments described herein are notlimited in their application to the details of the teachings anddescriptions set forth, or as illustrated in the accompanying figures.Rather, it will be understood that the present embodiments andalternatives, as described and claimed herein, are capable of beingpracticed or carried out in various ways. Also, it is to be understoodthat words and phrases used herein are for the purpose of descriptionand should not be regarded as limiting. The use herein of such words andphrases as “including,” “such as,” “comprising,” “e.g.,” “containing,”or “having” and variations of those words is meant to encompass theitems listed thereafter, and equivalents of those, as well as additionalitems.

Accordingly, the foregoing descriptions of embodiments and alternativesare meant to illustrate, rather than to serve as limits on the scope ofwhat has been disclosed herein. The descriptions herein are not meant tolimit the understanding of the embodiments to the precise formsdisclosed. It will be understood by those having ordinary skill in theart that modifications and variations of these embodiments arereasonably possible in light of the above teachings and descriptions.

What is claimed is:
 1. A method to lower benzene levels in absorbentsthat are used for desulfurization of a gas flow in a reactor having aninlet and an outlet, comprising: applying at least one agent to theabsorbents, wherein the absorbents are aluminosilicate zeolites having astructure that contains at least one metal; and displacing benzene withthe at least one agent that reacts with the at least one metal; whereinthe at least one agent is water, and the weight percentage of water isabout 1% to about 60%.
 2. The method of claim 1, wherein the weightpercentage of water is about 10% to about 50%.
 3. The method of claim 1,wherein the at least one metal is copper.
 4. The method of claim 3wherein applying at least one agent to the absorbents comprises exposingthe absorbents to a hydrated gas stream.
 5. The method of claim 4,wherein the method is performed at a temperature no greater than about100° C.
 6. A method to lower benzene levels in absorbents that are usedfor desulfurization of a gas flow in a reactor having an inlet and anoutlet, comprising: applying at least one agent to the absorbents,wherein the absorbents are aluminosilicate zeolites having a structurethat contains at least one metal; and displacing benzene with the atleast one agent that reacts with the at least one metal; wherein the atleast one agent is chosen from the group benzyl alcohol, benzaldehyde,methanol, and diethyl ether.
 7. The method of claim 6, wherein the atleast one agent is benzyl alcohol, and the weight percentage of benzylalcohol is about 1% to about 60%.
 8. The method of claim 7, wherein theweight percentage of benzyl alcohol is about 10% to about 50%.
 9. Themethod of claim 6, wherein the at least one metal is copper.
 10. Themethod of claim 9, wherein applying at least one agent to the absorbentscomprises exposing the absorbents to a hydrated gas stream.
 11. Themethod of claim 6, wherein the weight percentage of the at least oneagent is about 30% to about 60%.
 12. The method of claim 11, whereinapplying at least one agent to the absorbents comprises exposing theabsorbents to a hydrated gas stream.
 13. The method of claim 12, whereinthe method is performed at a temperature no greater than about 100° C.14. A method to lower benzene levels in absorbents that are used fordesulfurization of a gas flow in a reactor having an inlet and anoutlet, comprising: applying at least one agent to the absorbents priorto or after installation of the absorbents in a reactor but before use,wherein the absorbents are aluminosilicate zeolites having a structurethat contains at least one metal; then lowering the amount of benzenethat interacts chemically with the at least one metal when the at leastone agent reacts with the at least one metal, wherein the at least oneagent is chosen from the group water, benzyl alcohol, benzaldehyde, anddiethyl ether, and the weight percentage of the at least one agent isabout 30% to about 60%.
 15. The method of claim 14, wherein the weightpercentage of the at least one agent is about 40% to about 50%.
 16. Themethod of claim 14, wherein the at least one metal is copper.
 17. Themethod of claim 14, wherein the at least one agent is water, andapplying at least one agent to the absorbents comprises exposing theabsorbents to a hydrated gas stream.